Force sensing apparatus

ABSTRACT

A force sensing apparatus comprising: a plate-like strain producing body; a central portion disposed integrally at a center of the body and having higher rigidity than the body; a peripheral portion disposed integrally along a periphery of the body and having higher rigidity than the body; and a plurality of sensing elements formed on a surface of the body and having an electric resistance variable in accordance with a deformation thereof in order to simultaneously sense mutually orthogonal X, Y and Z axial components of an external force applied to the body via the central portion or the peripheral portion, the sensing elements being on the same plane.

This is a division, of application Ser. No. 07/073,290, filed Jul. 14,1987, now Pat. No. 4,836,034.

FIELD OF THE INVENTION

This invention relates to a force sensing apparatus used inthree-dimensional input devices, for example, robots and man-machineinterfaces.

BACKGROUND OF THE INVENTION

A conventional force sensing apparatus includes a strain producing bodywhich is elastically deformed when an external force is applied theretoand a plurality of sensing elements formed on the body and having anelectric resistance changing in accordance with a deformation of thebody. This apparatus takes out a change of the electric resistance as anelectric signal of those sensing elements to sense the applied externalforce.

Generally, in a force sensing apparatus of this type, an external forceacts on a point of action and can be decomposed into a number ofcomponents in accordance with the direction in which the external forceacts.

There are several force sensing apparatuses which include a strainproducing body of a cubic block structure which separately sensesrespective components of an external force applied thereto. These aredisclosed in Laid-Open Utility Model Application Nos. 11903/1979 and21021/1979, Laid-Open Patent Application Nos. 95433/1984, 57825/1986,79129/1986, etc. Especially, these applications are characterized inthat the force components Fx, Fy and Fz in the directions of X, Y and Zaxes and the moment components Mx, My and Mz around the X, Y and Z axesof the external force are separately sensed by strain gauges attached onseveral surfaces to which the directions of the corresponding forcecomponents are perpendicular respectively. Thus the strain producingbody cannot avoid taking the form of a three-dimensional structure as ablock structure, as described above.

So long as such structure is concerned, means for manufacturing thestrain producing body is limited to metal machining and/or electricdischarge machining techniques. This means that it is necessary tomanufacture the body from a block-like workpiece, which is difficult andtroublesome. Further, such strain gauges attached so as to sense thecorresponding force components must to be electrically connected in abridge circuit, which means that the wiring is troublesome. Thus it isdifficult to make them compact and reduce the manufacturing cost, andproductivity is low accordingly.

Another example is a cubic block of combined plates, etc., to separatelysense the respective external force components, as disclosed inLaid-Open Patent Application No. 83929/1986. A problem in this structureis that reproductivity is low because the sensing surfaces for therespective force components are fastened by screws, etc., which islikely to cause a hysteresis or non-linearity due to a deformation ofthe fastened surface portions.

OBJECTS OF THE INVENTION

It is a first object of this invention to provide a force sensingapparatus in which the strain producing body is easy to manufacture andthe sensing elements are also easy to manufacture.

It is a second object of this invention to provide a force sensingapparatus in which the strain producing body and the sensing elementsare easy to manufacture and interferences in respective force componentsof the applied force are very small.

SUMMARY OF THE INVENTION

The first object of this invention is achieved by a force sensingapparatus comprising:

a plate-like strain producing body;

a central portion disposed integrally at a center of the body and havinghigher rigidity than the body;

a peripheral portion disposed integrally along a periphery of the bodyand having higher rigidity than the body; and

a plurality of sensing elements formed on a surface of the body andhaving an electric resistance variable in accordance with a deformationthereof in order to simultaneously sense mutually orthogonal X, Y and Zaxial components of an external force applied to the body via thecentral portion or the peripheral portion, the sensing elements being onthe same plane.

The second object of this invention is achieved by a force sensingapparatus comprising:

a plate-like strain producing body;

a central portion disposed integrally at a center of the body and havinghigher rigidity than the body;

a peripheral portion disposed integrally along a periphery of the bodyand having higher rigidity than the body;

a plurality of sensing elements formed on a surface of the body andhaving an electric resistance variable in accordance with a deformationthereof in order to simultaneously sense mutually orthogonal X, Y and Zaxial components of an external force applied to the body via thecentral portion or the peripheral portion; and

a plurality of holes provided along a circumference of a circle betweenthe central portion and the peripheral portion, the sensing elementsbeing on the same plane.

According to this invention, as described above, a flat plate-likestrain producing body is provided in which either the central portion orthe peripheral portion thereof is used support portion and the otherportion is use for action. A sensing surface is formed between thecentral portion and the peripheral portion, both of which have a higherrigidity than that of the sensing surface. Sensing elements are formedon the sensing surface of the strain producing body and exhibit anelectric resistance variable in accordance with a mechanical change inthe sensing surface. Therefore, a first effect is that the flatplate-like strain producing body is very easy to manufacture using amanufacturing method such as press working of fine blanking or casting,which cannot be used on a block-like workpiece in the prior art. Sensingelements can be formed from a thin semiconductor film, so that sensingelements having equal characteristic can be arranged at exact positions.Especially, wiring of complex leads for a bridge circuit is easy.

A second effect is that, when the sensing surface is deformed, the holesdisposed in the sensing surface intercept a circumferential bendingstress to reduce interference between the respective components tothereby provide force sensing with high reliable accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

A force sensing apparatus of this invention will be described byreferring to FIG. 1 to FIG. 20.

FIG. 1 is a perspective view of a first embodiment of this invention;

FIG. 2 is a plan view of the embodiment;

FIG. 3 is a cross-sectional view taken along the line III--III of FIG.2;

FIG. 4 is a cross-sectional view taken along the line IV--IV of FIG. 2;

FIG. 5 is an electric circuit diagram showing a bridge circuit forsensing a moment component My;

FIG. 6 is an electric circuit diagram showing a bridge circuit forsensing a moment component Mx;

FIG. 7 is an electric circuit diagram showing a bridge circuit forsensing a force component Fz;

FIGS. 8(a) and (b) are side views showing the principles of the sensing;

FIGS. 9(a), (b), and (c) are side views showing the principles ofsensing when an external force is applied to the flat plate strainproducing body;

FIG. 10 is a perspective view, showing directions of components of aforce;

FIGS. 11(a), (b), (c) and (d) are side views of the plate-like bodydeformed by a moment My exerted thereon;

FIGS. 12(a), (b), (c) and (d) are side views of the plate-like; bodydeformed by a moment Mx exerted thereon;

FIGS. 13(a), (b), (c) and (d) are side views of the plate-like bodydeformed by a force Fz exerted thereon;

FIG. 14 is a vector diagram showing the respective components of anexternal force exerted on the body;

FIG. 15 is a perspective view of a second embodiment of this invention;

FIG. 16 is a plan view of a third embodiment of this invention;

FIG. 17 is a plan view of a modification;

FIG. 18 is a plan view of a further modification;

FIG. 19 is a perspective view of a fourth embodiment of this invention;and

FIG. 20 is a cross-sectional view taken along the line C-C in FIG. 19.

DETAILED DESCRIPTION OF THE PRESENT PREFERRED EMBODIMENT

A first embodiment of this invention will now be described withreference to FIGS. 1 to 14. A flat plate-like strain producing body 1includes an annular thick peripheral portion 2 having high rigidity andalso having eight mounting holes 3 arranged along the circumference ofthe same circle and extending through the thickness of the body 1thereof. The peripheral portion 2 is connected to a support 4 which isfixed to a fixture, not shown.

The body 1 has a thick disc-like central portion 5 which has fourmounting holes 6 extending through the thickness thereof and which isattached to a member, not shown. The central portion 5 is used as aportion of action 7 on which an external force acts.

A thin flat plate portion 8 is formed between the peripheral portion 2and the portion of action 7, and a surface of the plate portion 8 isused as a sensing surface 9. The plate portion 8 has eight relativelylarge holes 10 arranged at equal intervals which define eight radialarms 11 which connect the peripheral portion 2 and the central portion5. Each arm 11 includes the narrowest central portion 12 and twoexpanding portions 13 in the form of a substantial trapezoid, being ateach end of the central portion 12 respectively.

As shown in FIG. 2, sensing elements 14 of strain gauges labelled Y1,Y2, Y3 and Y4 are formed on the X axis on the expanding portion 13.Sensing elements Y1, Y4 are positioned on the outer expanding portion13, while sensing element Y2, Y3 are positioned on the inner expandingportion 13. These sensing elements 14 are connected to form a bridgecircuit as shown in FIG. 5 so that, when the balance among Y1, Y2, Y3and Y4 is lost, an output Vy will be produced.

Sensing elements 14 of strain gauges labelled X1, X2, X3 and X4 areformed on the Y axis orthogonal to the X axis on the expanding portion13. Sensing elements X1, X4 are positioned on the outer expandingportion 13 while sensing elements X2, X3 are positioned on the innerexpanding portion 13. These sensing elements 14 are connected to form abridge circuit as shown in FIG. 6 so that, when the balance among X1,X2, X3 and X4 is lost, an output Vx will be produced.

Eight sensing elements 14 labelled Z1, Z2, Z3, Z4, Z5, Z6, Z7, Z8 ofstrain gauges are formed on the expanding portions 13, in order that Z1,Z2, Z3, Z4 are disposed on the Z' axis and Z5, Z6, Z7, Z8 are disposedon the Z" axis, the Z' and Z" axes being at 45° to the X and Y axes. Z1,Z4, Z5, Z8 are positioned on the outer expanding portion 13 while Z2,Z3, Z6, Z7 are positioned on the inner expanding portion 13. Theseelements 14 are connected as shown in FIG. 7, namely, pairs Z1, Z4; Z2,Z3; Z5, Z8; and Z6, Z7 are connected to form a bridge circuit so thatwhen the balance among these pairs is lost, an output Vz will beproduced.

The sensing elements 14 positioned as described above may be of aconventional strain gauge of a metal foil, but, in this embodiment, theyare formed by a thin film technique. The plate-like strain producingbody 1 is made of an aluminum alloy or stainless steel. The sensingsurface 9 has a buffer layer deposited thereon. Specifically, the bufferlayer is of an Si₃ N₄ or a virtually internal stress-free SiOx filmhaving a thickness of from 2000Å to 10000 Å formed by plasma CVD(chemical vapour deposition). A thin semiconductor film having athickness of from 5000 to 20000 Å is then superposed on the bufferlayer, and a high conductive material for an electrode material (forexample, a thin metal film of Al, Ni-Cr, or Mo) having a thickness offrom 2000Å to 5000 Å is further superposed. Specifically, the thinsemiconductor film made of μc-Si (microcrystal silicon) or n+ a--Si(amorphous silicon) formed by plasma CVD. or optical excitation CVD, andthe electrode is made of Al-Si (Si: 2-3% by weight) formed by vapourdeposition or sputtering.

The electrode material is then patterned into a predetermined format byphotolithography or etching. For etching, either a wet process or a dryprocess may be used. However, in order to avoid an influence on thecharacteristic of the elements, dry etching is more preferable. When thethin semiconductor film is made of n⁺ a-Si:H, and a mixture gas of CF₄-O₂ (3-20% by weight) is used in the plasma etching device, good etchingwill be possible with high reproductivity and high accuracy.

The wiring density is high because of bridge circuits of sensingelements 14 needed for sensing Fx, Fy, Fz, Mx, My and Mz components,which requires multilayered wiring, in which an inter-layer insulatingmaterial (for example, of photosensitive polyimide or Si₃ N₄) issuperposed. When photosensitive polyimide is to be used, it is coated bya roll coater or a spinner, and contact holes are formed byphotolithography or etching. When Si₃ N₄ is to be used, the inter-layerfilm is formed by plasma CVD, and then resist is coated and contactholes are formed by photolithography or etching.

A second electrode material (for example, of Al, Ni-Cr or Mo) is furthersuperposed on that insulating material and predetermined wiring and padsare formed by photolithography or etching.

In order to improve the damp-proofness and prevent possible damage, apassivation film (for example, of parylene or SiO₂, Si₃ N₄,) issuperposed.

The first electrode pattern, inter-layer insulating material, and secondelectrode pattern may be formed earlier. In this case, removingdefective articles manufactured up to this process would improve theyield in the final process. In the total defectiveness of sensingelements 14 shortcircuits and disconnections between the first and thesecond electrode patterns form 25% and shortcircuits due to badinsulation in the inter-layer insulating material and disconnections dueto bad contact holes form 20%. These defects up to this process occupythe majority of the defects as mentioned above. Therefore, it bringsabout a big effect to remove these defects at an early process.

When a thin semiconductor film is superposed, a metal mask havingnecessary openings therein may be used to form thin semiconductor filmsonly at the predetermined positions. This eliminates thephotolithographic and etching processes onto the thin semiconductorfilm, thereby simplifying the processes and reducing the cost inmanufacturing the sensing elements 14.

The sensing principles of the plate-like strain producing body 1 havingthe above-mentioned constitution will be described with reference toFIGS. 8(a), (b). First, in FIG. 8, a strain producing body 15 comprisinga beam or a plate is mounted between a fixed member 16 and a movablemember 17. Sensing elements of strain gauges 18 are disposed on theupper and lower surfaces of the body 15 at an equal distance from thecenter of the body 15. FIG. 8(a) shows the state in which no load isapplied to the movable member 17, and FIG. 8(b) shows the state in whicha downward load F is applied to the movable portion 17 to move the samedownwardly. At this time, body 15 is extended at its upper surface andcontracted at its lower surface near the fixed member 16, while it iscontracted at its upper surface and extended at its lower surface nearthe movable member 17. Thus strains having opposite signs ± and the sameabsolute value occur on the corresponding strain gauges 18, and hencethe resistances of the strain gauges 18 vary accordingly. Generally,these four strain gauges 18 are connected to form a bridge circuit whichproduces an output four times as high as that of a single strain gauge.

FIG. 9 shows a plate-like strain producing body 1 similar in crosssection to body 1 in this embodiment. The peripheral support 4 is fixedto a fixture, not shown, and an external force is to act on the centralportion of action 7. FIG. 9(a) shows the state in which no load acts onthe portion of action 7, while FIG. 9(b) shows the state in which avertical load Fz acts on the central portion 7. Under this condition,one side of FIG. 9(b) is similar to FIG. 8(b) wherein two inner sensingelements 14 are contracted (-), while two outer sensing elements 14 areextended (+). FIG. 9(c) shows the state in which a moment M acts on theportion of action 7. Under this condition, inner and outer sensingelements 14 show opposite signs.

In this plate-like strain producing body 1 with such principles, sincethe support 4 and the portion of action 7 have large thickness comparedto that of the flat plate portion 8, and since they are formedintegrally, the support 4 and the portion of action 7 have higherrigidity compared to that of the flat plate portion 8. Therefore, onlythe flat plate portion 8 is strained when the portion of action 7receives force to be sensed, which makes measuring accuracy better. Astress (due to tightening of screws or the like) is likely to occur inthe support 4 and the portion of action 7, which produces a strain inthe sensing surface 9. However, according to this invention, the support4 and the portion of action 7 have sufficient rigidity; so that nostrain due to the tightening will be produced on the sensing elements14.

Generally, a pressure receiving member projecting in the Z axialdirection is attached to the central portion of action 7. If a force Fxis applied to an end of the pressure receiving member, a moment My willbe produced at the portion of action 7 while, if a force Fy is appliedto the end of the pressure receiving member, a moment Mx will beproduced at the portion of action 7. Therefore My, Mx and Fz are threerepresentative components.

The relationship among the components will be described with referenceto FIG. 10. First assume that there is a point of action O0 at thecenter of the sensing surface 9 on which a pressure receiving memberhaving a height L is attached and that an external force acts on a pointof action O1 of the pressure receiving member. The components Fx, Fy,Fz, Mx, My which act on the point of action O1 of the pressure receivingmember are converted into components Fz, Mx, My on the point of actionO0 of the sensing surface 9.

A typical state in which an external force acts on the strain producingbody 1 will be described with reference to FIGS. 11--13. First, FIG.11(a), (b), (c), (d) show the state in which a moment My only acts onthe portion of action 7. Under this condition, as shown in FIG. 11(a),there is no change in the Mx component sensing portion, and the bridgecircuit composed of sensing elements 14 labelled X1, X2, X3, X4, asshown in FIG. 6, provides a null output Vx. The My component sensingportion is in a mode shown in FIG. 11(b) where the respective sensingelements 14 labelled Y1, Y2, Y3, Y4 are deformed, and the bridge circuitshown in FIG. 5 provides an output Vy corresponding to the moment My.The Fz component sensing portion is in a mode shown in FIG. 11(c), (d)in which eight sensing elements 14 labelled Z1, Z2, Z3, Z4, Z5, Z6, Z7,Z8 are deformed. The extent to which the respective sensor elements aredeformed is small, and the output of the bridge circuit shown in FIG. 7is virtually null. Namely, each of pairs Z1, Z4; Z2, Z3; Z5, Z8; Z6, Z7provides opposite extensions and contractions and the resultantresistances of the respective arms of the bridge circuit of FIG. 7 arecancelled to zero to thereby provide a null output Vz.

Although eight strain gauges are used for sensing the Fz component, fourstrain gauges may be used which are formed on either one of axes atangles of 45° to the X and Y axes. However, in order to reduceinterference by forces (moments) except for the Fz component, the8-strain gauge system is preferable used.

The state in which only moment Mx acts is shown in FIG. 12(a), (b), (c),(d) in which the Mx component sensing portion produces output Vx whilethe My component sensing portion outputs a null output Vy. The output Vzof the Fz component sensing portion becomes null for a reason similar tothat in FIG. 11(c), (d), as mentioned above.

The state in which only a force Fz acts is shown in FIG. 13(a), (b),(c), (d). In the Mx component sensing portion X1, X4 exhibitdeformations of extension (+) while X2, X3 exhibit deformations ofcontraction (-), so that the bridge circuit of FIG. 6 produces a nulloutput Vx. By the similar reason, the My component sensing portionproduces a null output Vy. On the other hand, the Fz component sensingportion produces an output Vz four times as high as that of singlesensor element 14. These outputs of respective component sensingportions shown in FIGS. 11--13 are collected as shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                            My     Mx    Mz                                           ______________________________________                                        Mx component sensing portion                                                                      X1    0        +   +                                                          X2    0        -   -                                                          X3    0        +   -                                                          X4    0        -   +                                                          Vx    0        Vx  0                                      My component sensing portion                                                                      Y1    -        0   +                                                          Y2    +        0   -                                                          Y3    -        0   -                                                          Y4    +        0   +                                                          Vy    Vy       0   0                                      Fz component sensing portion                                                                      Z1    -        -   +                                                          Z2    +        +   -                                                          Z3    -        -   -                                                          Z4    +        +   +                                                          Z5    -        +   +                                                          Z6    +        -   -                                                          Z7    -        +   -                                                          Z8    +        -   +                                                          Vz    0        0   Vz                                     ______________________________________                                    

As described above, it becomes possible to amplify the signals to besensed of the sensing elements 14, and to nullify other interferentialsignals by the bridge circuit.

Since the large holes 10 are formed in the plate portion 8 of the strainproducing body 1, the respective components are well separated. If theplate portion 8 should have no holes 10 and be formed by a circulardiaphragm, a bending stress would be produced circumferentially as wellas radially with substantially equal magnitudes in the plate portion 8when an external force acts on the portion of action 7. Thecircumferential stress would greatly interfere with the other componentswhen the same components are to be sensed. Since, as described above, aplurality of holes 10 are formed at equal intervals along thecircumference of a circle as described above, however, thecircumferential bending stress produced in the plate portion 8 isreduced so that a strain will appear mainly radially.

The arms 11 are defined by the holes 10 formed in the plate portion 8 ofthe strain producing body 1, and the sensing elements 14 are positionedat the corresponding expanding portions 13 of the arms 11. Eachexpanding portion 13 is defined by adjacent holes 10 and takes the formof a substantial trapezoid. Each expanding portion 13 is separately by ahole 10 from each adjacent expanding portion 13, and it consequentlydoes not invite interference by a circumferential bending stress, asdescribed above. Since each expanding portion 13 is positioned at thebase portion of an arm 11 where a radial bending stress is easy tooccur, it is proper to form the sensing elements 14 on the expandingportion 13 for sensing a strain due to the applied external force. Thedistribution of bending stresses occurring at the expanding portion 13is relatively uniform and causes no interference. Therefore, when thesensing elements 14 are attached as a strain gauge to the strainproducing body 1, there is no deterioration in the precision of thesensing, although the sensing elements are slightly deviated from theirtarget positions. Thus slight deviation in position can be tolerated,and no severe conditions are required for the accuracy in positionswhere the sensing elements 14 are attached.

Provision for eight holes in the plate portion 8 of the strain producingbody 1 allows the sensing elements 14 labelled Z1, Z2, Z3, Z4, Z5, Z6,Z7, Z8 to be disposed on the Z' and Z" axes, respectively at 45° to theX and Y axes. Such arrangement of the sensing elements 14 allows the Fzcomponent to be sensed well as shown in the Table.

The number of holes 10 may be a multiple of 8. It is not necessarilyrequired to dispose the sensing elements 14 on the axes at angles of 45°to the X and Y axes. The sensing elements 14 may be disposed at otherdesired angles. But if the number of holes 10 is a multiple of 8, thesensing elements 14 can be disposed symmetrically along thecircumference of a circle so that variations of the resistances of thesensing elements are counterbalanced.

The Second Embodiment

A second embodiment of this invention will be described with referenceto FIG. 15. This embodiment is the same in structure as the firstembodiment except for the sensing elements 14 being attached to thecorresponding inner peripheries 19 of holes 10 in strain producingbody 1. The Fy sensing elements 14 are attached to the inner periphery19 of each arm 11 along the X axis, the Fx sensing elements 14 areattached to the inner periphery 19 of each arm 11 along the Y axis, andthe moment Mz sensing elements 14 are attached to the inner periphery 19of each arm 11 along the Z axis at angles of 45° to the X and Y axes.Therefore, according to this embodiment, the moment Mz around the Z axiscan be also sensed.

The Third Embodiment

FIG. 16 shows a third embodiment of this invention in which the holes 10are oval with the longer diameter being oriented radially.

FIG. 17 shows a modification of the third embodiment in which oval holes10 are oriented differently from those in FIG. 16; the holes aredisposed so that their shorter diameters are oriented radially.

FIG. 18 shows a further modification of the third embodiment in whichthe holes 10 are hexagonal. From the foregoing, it will be seen that theshape of; the holes 10 may be optional.

The Fourth Embodiment

A fourth embodiment of this invention will now be described withreference to FIGS. 19 and 20. In this embodiment, no holes 10 are formedin the plate portion 8 of the strain producing body 1, the sensingelements 14 are arranged on the orthogonal X and Y axes for sensing Myand Mx, respectively, and also on Z' and Z" axes at angles of 45° to theX and Y axes for sensing Fz.

While in the above respective embodiments, the plate-like strainproducing body 1 has been described as being a disc, the shape of thebody is not limited to a disc, but may be square, rectangular, polygonalor of any other optional shape.

While the above embodiments have been described as sensing all thecomponents in three directions X, Y and Z axes, the sensing apparatusmay be constructed so as to sense the components in only two directionsfor on the X and Y axes.

What is claimed is:
 1. A force sensing apparatus comprising:(a) a plate-like body having a central portion, a peripheral portion, and a sensing portion connecting said central portion with said peripheral portion and having one flat surface, said sensing portion having lower rigidity compared to each of said central portion and said peripheral portion; (b) a first sensing element disposed on an X axis extending on said one flat surface for sensing a moment around a Y axis extending on said one flat surface orthogonally to said X axis; (c) a second sensing element disposed on said Y axis extending on said one flat surface for sensing a moment around said X axis; and (d) a third sensing element and a fourth sensing element respectively disposed on a Z' axis and a Z" axis extending on said one flat surface for sensing a force in the direction of a Z axis extending perpendicularly to said X, Y, Z', and Z" axes; (e) said first, second, third, and fourth sensing elements being formed on only said one flat surface.
 2. A force sensing apparatus according to claim 1, in which said Z' and Z" axes extend on said one flat surface orthogonally with respect to each other and at angle of 45 degrees to the X and Y axes respectively.
 3. A force sensing apparatus according to claim 2, in which a plurality of holes are provided along a circumference of a circle on said one flat surface in order to separate X and Y axial components of forces to be sensed.
 4. A force sensing apparatus according to claim 3, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 5. A force sensing apparatus according to claim 3, in which the number of holes is 8 or a multiple of
 8. 6. A force sensing apparatus according to claim 5, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 7. A force sensing apparatus according to claim 5, in which each of said sensing elements is formed on an expanding portion:(a) in said one flat surface defined by two adjacent holes and (b) in which a distribution of stresses is uniform.
 8. A force sensing apparatus according to claim 7, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 9. A force sensing apparatus according to claim 2, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 10. A force sensing apparatus according to claim 1, in which a plurality of holes are provided along the circumference of a circle on said one flat surface in order to separate X and Y axial components of forces to be sensed.
 11. A force sensing apparatus according to claim 10, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 12. A force sensing apparatus according to claim 10, in which the number of holes is 8 or a multiple of
 8. 13. A force sensing apparatus according to claim 12, in which each of said sensing elements is formed on an expanding portion:(a) in said one flat surface defined by two adjacent holes and (b) in which a distribution of stresses is uniform.
 14. A force sensing apparatus according to claim 13, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 15. A force sensing apparatus according to claim 12, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film.
 16. A force sensing apparatus according to claim 1, in which:(a) said body is made of aluminum alloy or stainless steel and (b) each of said sensing elements is made of a semiconductor film. 